17.5.8 MySQL Cluster Single User Mode

Single user mode enables the database
administrator to restrict access to the database system to a
single API node, such as a MySQL server (SQL node) or an instance
of ndb_restore. When entering single user mode,
connections to all other API nodes are closed gracefully and all
running transactions are aborted. No new transactions are
permitted to start.

Once the cluster has entered single user mode, only the designated
API node is granted access to the database.

After this command has executed and the cluster has entered single
user mode, the API node whose node ID is 5
becomes the cluster's only permitted user.

The node specified in the preceding command must be an API node;
attempting to specify any other type of node will be rejected.

Note

When the preceding command is invoked, all transactions running
on the designated node are aborted, the connection is closed,
and the server must be restarted.

The command EXIT SINGLE USER MODE changes the
state of the cluster's data nodes from single user mode to normal
mode. API nodes—such as MySQL Servers—waiting for a
connection (that is, waiting for the cluster to become ready and
available), are again permitted to connect. The API node denoted
as the single-user node continues to run (if still connected)
during and after the state change.

Example:

ndb_mgm> EXIT SINGLE USER MODE

There are two recommended ways to handle a node failure when
running in single user mode: